Physiological aspects of senescence are investigated with germfree animals. The effect of microbial flora, one of important environmental factors, is studied in terms of longevity and decline of physiological functions. A series of longitudinal studies will be conducted on several physiological functions with germfree animals and conventional counterparts. Cross-sectional studies will be carried out in regard to cardiac, renal, homeostatic and biochemical functions with aged and adult germfree rats with corresponding conventional controls. Modification of peculiarities accompanying germfree condition will be tested with respect to aging. It will be attempted to evaluate the hierarchical order in the deterioration of physiological functions in determining longevity.